Glaciers

What comes to mind when you think of a glacier? If “constant movement” was your answer, then you’re spot on. While glaciers may appear as solid, formidable sentinels of the mountains, they are actually in constant motion. 

Bomber Glacier in Alaska, named for wreckage on the glacier from a plane that crashed in 1957.

Various features form the basic anatomy of a glacier. The point of a glacier which is farthest from the origin is known as the terminus or toe. Surrounding a glacier are moraines, which are areas of rock and debris (or “glacial till”) that are deposited around a glacier as it retreats. Lateral moraines are located at the sides of a glacier, while terminal moraines are located at the toe. Some glacial features can be hazardous to human travel. Crevasses are V-shaped cracks that form with the movement of brittle ice. Vertical shafts called moulins can form in a glacier as meltwater from the surface flows deep within the glacier. When traveling on glaciers you’ll want to be on the lookout for these features, as they can be very deep.

Glaciers form gradually when snow accumulates in an area faster than the rate of summer snowmelt. The weight of this collected snow puts pressure on the accumulated snowpack, transforming it into ice. When the buildup of snow and ice becomes very thick, the force of gravity carries the mass downslope. Ice at the bottom of a glacier tends to move more slowly than ice at the top because it experiences greater frictional forces. During surges, these rivers of flowing ice can move multiple meters per day, which is pretty fast for a gigantic mass of material.

Castner Glacier in Alaska. You can see lateral moraines along the sides of the glacier, where material has been deposited.

It may feel like we are far from glacial features here in Minnesota, but that is not the case. Glaciers existed here just 10,000 years ago, which is really not very long in geologic time. The geology of Minnesota has been influenced by multiple periods of glaciation, as ice sheets expanded and retreated with changes in climate. We have glaciers to thank for our abundance of lakes, which formed as the land was carved by glacial forces.

Today, many of the world’s glaciers are retreating rapidly in response to a warming climate. If you’d like to learn more about these impressive features, the U.S. Geological Survey Benchmark Glacier Project has studied glaciers in the field for decades. You can also learn more about glacial features by wandering into your own backyard; if you’re lucky, you may find evidence of a glaciated past.

The author’s partner heading up Penny Royal Glacier in Alaska.